Cellulosic pellicle



name May 1, 1940 UNITED STATES P TENT OFFICE CELLULOSIO PEHJOLE William Frederick Underwood, Buffalo, N. Y., as-

sia'nor to E. I. du Pont de Nemours &

Company,

Wilmington, Del., a corporation of Delaware No Drawing.

Application March 17, 1937,

Serial No. 131,531 I 5 Claims.

This invention relates to cellulosic structures, and more particularly it relata to a method for softening cellulosic structures by the incorporation therein of softening agentsand the product resulting therefrom.

-may find certain uses, the softened and therefore flexible sheet or film is much more generally useful. Heretofore, as softeners for regenerated cellulose pellicles, the art has employed such substances as ethylene glycol, propylene glycol, diethylene glycol, glycerol, and the like, but, of these, by far the most important is glycerol which has hitherto known no equal as a softening agent for producing flexible, transparent and durable cellulosic pellicles such as those of regenerated cellulose. Despite the numerous advances which have been made in the production 'and development of cellulosic pellicles, no softening agent has thus far been found which can be successfully applied as a substitute for glycerol without seriously restricting the utility of the product.

- Glycerolis ,obtained commercially primarily as a by-product from the soap industry. As a byproduct, the quantity may be limited and hence glycerol is subject to market fluctuation of supply as well as price. The glycols, mentioned above as useful cellulose softeners, are for the most part obtained synthetically and consequently they are relatively expensive. For an industry consuming large amounts of these materials, therefore, the development of less expensive equivalents or means for reducing the consumption of expensive materials will lead to marked. economies in production.

It has now been found that particularly desirable softness can be imparted to cellulosic structures of the type above referred to by the incorporation therein of a water-soluble hydroxyalkyl derivative ofammonia. This substance may replace glycerol in whole orin part as will appear more specifically hereinafter.

It is therefore an object of this invention to provide a new and useful method for preparing cellulosic pellicles having a satisfactory rigidity, elongation, flexibility, durability and transparency.

It is a further object of this invention to pro- 10 vide a cellulosic pellicle treated with a softening agent which will not interfere with any subsequent treatment of the cellulosic pellicle, such as the application of surface coatings, ink, coloring matter, adhesives, or the like.

A still further object of this invention is to 15- provide a rigid, flexible, transparent, durable, cellusosic pellicle such as a sheet or film of regenerated cellulose suitable for use as a wrapping tissue, treated with a softening agent comprising a hydroxyalkyl derivative of ammonia. 20

Other objects of the invention will appear hereinafter.

-By the term "rigidity or its equivalentas used herein is meant that property which is the opposite of' limpness, in other words, rigidity in 25 I the sense that the pellicle can be advanced in a wrapping machine or similar apparatus without curling, crumpling, or otherwise fouling th machine.

The term "durability is used to define resistance to shock or rough handling. Thus, for example, bags may be fabricated from the pellicles and filled with some standard material such as a certain weight of dried beans and the package sealed, whereupon the durability may be measured against a known standard by tumbling the package under standard conditions and noting the resistance to breakage'of the wrapper. 40

The objectsof this invention can be attained generally by substituting a hydroxyalkyl derivative ofammonia having a boiling point of at least 175 C. at a pressure of 760 mm. of mercury and a solubility of at least 5% in water at a temperature of -70 C., for glycerol as a softening agent. The hydroxyalkyl derivative of ammonia can be substituted in whole or in part for the glycerol. 7 50 .tures of similar character.

As a base, the invention contemplates the use of any cellulosic structure, particularly sponges and structures of pellicular nature such as a sheet or film, artificial straw, cap, band or continuous tube, such as may be obtained by the coagulation and/or regeneration from an aqueous cellulosic dispersion in accordance with the procedure customary to the art. Thus, the invention comprehends the use of regenerated cellulose pellicles such as may be obtained from the viscose or cuprammonium processes, glycol cellulose, cellulose'glycollic acid, lowly esterified or lowly etherified cellulose derivatives where there is only one ether or ester group associated with several cellulose units, and other cellulosic struc- Similarly, various types of paper, especially of the glassine type may be used as base materials. As a matter of convenience, the invention will be described in terms of its application tothe softening of regenerated cellulose pellicles such as those sheets or films of regenerated cellulose which aresuitable-for use as wrapping tissues.

In the manufacture of regenerated cellulose sheets or films, as for example by the viscose process, the cellulosic dispersion is cast through suitable apparatus into coagulating and/or regenerating baths from which it is finally obtained in the form of a continuous cellulosic sheet which is customarily led in a continuous manner through a series of purifying, bleaching and washing operations. Just prior to the drying operation which is also usually continuous and coordinated with the casting operation, the film is passed through a bath containing a softeningagent in such concentration that after the excess liquid has been removed from the surface of the sheet by suitable squeeze rolls and the excess moisture removed by passage through the drier, the final sheet can be wound up in a continuous fashion and will contain an appropriate predetermined amount of softening agent. The commercially available regenerated cellulose film contains approximately 4-8% moisture and depending upon the particular uses to which the product is destined, the softening agent, usually glycerol, may vary from about 8-25%, based on the combined weight of the cellulose and softening agent in the sheet.

The invention contemplates subjecting the base sheet or film to a bath containing a hydroxyalkyl derivative of ammonia in aqueous solution or in solution in an organic solvent. After treatment with the solution, the base is dried and may subsequently be provided with a surface coating, such as a moistureproof film or coating. Furthermore, when the softening agent is soluble in the solvent of the surface coating, the base may be treated with the softening agent simultaneously with the application of the coating composition. In this latter case, the softening agent to be applied simultaneously with the coating solution, is added or incorporated in the coating composition.

The quantity of hydroxyalkyl derivative of ammonia introduced into the base depends upon the composition of the base and the desired degree of flexibility in the final product and hence may vary within wide limits. Satisfactory results have been secured with a regenerated cellulose base when 5% to 19% and even up to or more, and preferably 15 to 18%, of the hydroxyalkyl derivative of ammonia is contained in the final product. The percentages stated above are based on the combined weight of cellulose and softener in the final product. When the total softener content of the final product is less than 5% it will not have the desired degree of softness, and when the product has a total softener content exceeding 19%, except in the case of heavy gage films, it often presents a slightly colored appearance which is usually objectionable. However, when the hydroxyalkyl derivative of ammonia is mixed with other softeners less than 5% of the former can be used to advantage. In order to obtain a material softening efiect from the hydroxyalkyl derivative of ammonia in mixtures of softeners it should constitute at least 10% of the total weight of the combined softeners. For example, when the mixed softener constitutes 15% of the total weightof the product at least 1.5% of the total weight should be hydroxyalkyl derivative of ammonia.

In accordance with the preferred form of this invention, a sheet or film of regenerated cellulose is passed through an aqueous bath containing the hydroxyalkyl derivative of ammonia, the excess bath being removed in any suitable manner, such as, for example, by squeeze rolls, wipers,

and the like, and the film dried subsequently thereto. Inasmuch as the softening agent contemplated by this invention is stable and substantially non-volatile at ordinary temperatures, it is immaterial whether or not a surface coating is applied thereto, nor is it material whether or not a surface coating is applied immediately after treatment with a softening agent or after a conin which the softener is dissolved, after which. the softening agent in solution is applied-there to. Where a solvent for a softener is used which is immiscible in water, the water will preferably first be removed by displacement with aninter mediate liquid material whichis miscible with both the softener solvent and water, after which the said intermediate material is displaced with a quantity of the softener solvent prior to treatment with the softener solution.

I The total amount of softener is controlled pri-.

marily by the total amount of softening agent in the treating bath, although thefilm thickness,"

wet pellicle, usually referred to as the gel sheet,

is impregnated with the-treating bathv and because of the large amount of water'associated with the cellulose, it is apparent that. the removal of this water during the drying operation will concentrate the softening agent with respect to the cellulose content of the pellicle. For example, if a regenerated cellulose pellicle containing about 15% total softener is desired as a final product, the concentration of the softener in the treating bath will be adjusted to approximately one-third that value, or about 5%. This is particularly true when the softening agents are substantially non-volatile and are not vaporized during the drying operation.

The following example will illustrate the practice of the invention, it being understood that the invention is not to be limited thereby:

Emample.--A, sheet or continuousfilm of Bel regenerated cellulose, which will hav'ea final 'dry thickness ofabout 0.0012", is immersed in or drawn through a bath consisting of a aqueous solution of triethanolamine. The sheet or film 'is-allowed to remain in contact with the bath for a time suiiicient to permit the establishmentof equilibrium (preferably not longer than five minutes) whereupon the excess liquid is removed by suitable devices such as scraper rods, squeeze rolls,

blotters or the like. The film is then dried in such -,a'manner as will maintain it substantially free from wrinkles, the drying temperature being of the order of 70 C.. The resultant film is clear, non-greasy and quite soft.

' The above example has been set forth in terms of I a sheet or film of gel'regenerated cellulose.

' Obviouslmthis is the more practical way of practicing the'invention since the softening agent is customarily incorporated into the sheet or film while vvthe latter is in the gel state and during the normal course of manufacture. If one desires to impregnate an already dried regenerated cellulose fihn with a softener of the character described, it is" possible to rewet the dried film so as to render it highly swollen, whereupon it may be treated with treating baths similar to those described but of' composition suitable for obtaining'thefinal product desired. In the san' e'way, a any of the sheets set forth as equivalent to regenerated cellulose sheets can be substituted in the specific example cited above formula: V

/N--ROH I I in which R, R1 and B: may be an aliphatic, aromatic, aromatic-aliphatic or. aliphatic-aromatic hydrocarbon radical, which'radicals may contain substituent groups or linkages, .such'as hydroxyl,

carbonyl, cyclic, amido, ke'to,-ether or thioether,

and in which R1 and R2 may be-an-acyl group or hydrogen; and the salts thereof. I

When R, R1 orRz are hydrocarbon radicals, it

is preferredthat such radicals contain not more I than six carbon atoms, and it is still further preferred that the total carbon atom content of R, R1 and R2 is not in excess of six carbon atoms.

As representative examples of types of hydroxy alkyl derivatives'of ammonia which may be used as a softening agent in accordance with the present invention maybe mentioned; I

'Homologues of mono-, diand triethanol amine By the term hydroxy alkyl derivative of am- I monia" as used throughout the specification and claims ismeant a substance having the general I such as mono-, diand tripropanol amine and mono-, diand tributanol, amine.

i n-n- -on-on v Benzylol amine Oir-om-om-on Ethylol phcnyl amino Plia'nylol amine (p-hydi'oxy plienyl amino) Diphcnylol amine (p-p' di hydroxy diphenyl amine) H Oz'q-om-om-on i N-CHr-OE cthylol pyridine N-OHr-OH I fi ctgl wpicollns (HO-CHr-GHDENEOOOQCOO Triethanolamlne bcnzoy nzoate l HO CH:NCH:(CHOH)|CH:0H

Mono-methylol glucamlne CHa-NGJHr-CHr-OH): Diethylol methyl amine Ha Isobutanol amine no-onr-on-om-z r-om-cn-onrou Di isobutanol amino orpholine ethanol As salts of the above compounds which have been found particularly desirable are the formate, glycollate, lactate, sulfate, HCl, oxalate, phosphate, acetate ricinoleate, linoleate and sulfonic salts thereof.

It is furthermore to be understood that two or more of the softening agents above mentioned may be used in combination with each other, or one or more of the above mentioned softening agents may be used in combination with one or more known softening agents, for example, a mixture of triethanolamine and glycerol in the ratio of 2:1 will operate to very good advantage. If a colored cellulosic pellicle is desired, it may be obtained in any of the ways commonly known in the art including the passage of the sheet or film through a bath containing a suitable dyestuff. If desired, the dyestufi may be added to the bath used for introducing the softening agent. In the same way, after the film has been treated with the softening agent, it may be subjected to any of the customary after-treatments such as sizing or coating, or the like, which may be customarily given to cellulosic pellicles of the type described in just the same manner that a glycerol softened regenerated cellulose film, for example, may be treated.

Since the softening agents of the presen invention. can be obtained synthetically, they are available in unlimited quantity independent of a natural source. The use of the newly described softening agents results in a product having satisfactory physical characteristics, particularly transparency, flexibility, durability, and the like.

The softeners set forth by this invention have been described in terms of their use in connection with the softening of cellulosic pellicles, but

it should be understood that such softeners are useful in other roles such as those normally played by such substances as glycerol.

Since it is obvious that various changes and modifications may be made in the above description without departing from the nature and spirit thereof, it is to be understood that the invention is not to be limited thereto except as set forth in the appended claims.

I claim:

1. A flexible, durable pellicle consisting of regenerated cellulose impregnated with softener therefor, said softener consisting of 15% to 18% of a hydroxyalkyl derivative of ammonia having a boiling point of at least 175 C. at a pressure of 760 mm. of mercury and a'solubility of at least 5% in water at a temperature of 60-70 C.

2. A flexible, durable pellicle consisting of regenerated cellulose and 15% to 18% triethanolamine as a softener therefor.

3. A flexible, durable pellicle consisting of regenerated cellulose impregnated with 15% to 18% softener thereof, said softener being .tripropanol v amine.

4. A flexible, durable pellicle consisting of regenerated cellulose impregnated with 15% to 18% softener therefor, said softener being tributano amine.

5. A flexible, durable pellicle consisting of regenerated cellulose sheet of about 0.0012 inch thickness impregnated with 15% of a softener therefor, said softener being triethanol amine.

WILLIAM FREDERICK UNDERWOOD. 

